An OLED is a self-emissive display device, and has received attention as a next generation display device with an advantage of not requiring a backlight for light emission, having a wide viewing angle, and having a high response speed as well. A constitution of a luminant part of such an OLED device generally comprises a transparent substrate, a transparent electrode layer, an organic light emitting layer, a metal electrode layer and, as necessary, an insulator film and a partition wall.
As the insulator film, inorganic materials such as silicon oxide or silicon nitride, or organic materials such as polyimide have been used in the art, and when forming the insulator film using common inorganic or organic materials, production costs increase since a multi-step process performing coating a photoresist (hereinafter, referred to as “PR”) on a substrate, exposure, PR development, etching and PR removing is generally required. In order to resolve such a problem, photosensitive polymers such as photosensitive polyimide, and the like, have been used as the insulator film (transparent bank). However, such an insulator film is transparent and thereby does not have a light-shielding property, and therefore, has a problem of reducing visibility by external light reflection of a metal electrode. Particularly, relative luminance and a contrast ratio rapidly decrease in the outdoors exposed to sunlight due to external light reflection.
In order to resolve such a problem of contrast ratio decrease, most existing OLEDs use a polarizing film on the surface of a substrate to reduce a contrast decrease caused by external light reflection. However, using a polarizing film blocks some of the light produced in an organic light emitting layer, and therefore, a luminance decrease may not be prevented.
When using a black bank in an insulator film of an OLED, a light-shielding property that has not been present in existing polyimide insulator films may be obtained, and external light reflection may be reduced, and there is no concern over a luminance decrease as well as costs are reduced since it is not required to use a polarizing film.
Particularly, a technology of obtaining a hole pattern using a narrow slit mask is important in developing a black bank for mobiles, and the hole pattern becomes an active area as an anode in an OLED structure. A device lifetime is reduced when residues are present in such a hole pattern and visibility becomes poor when straightness is not favorable. Using an existing Cardo-based binder has a problem of reducing straightness and causing residues in the hole.
Accordingly, research and development on a photosensitive resin composition for a black bank having improved hole residues and straightness have been continuously required in the art.